The invention relates to a manufacturing method for a donor film with improved surface roughness. The manufacturing method, comprising an additional heat-treatment process, produces a donor film capable of enhancing the lifetime of an end product and reducing the defect rate thereof.
In general, an organic electroluminescence device, which is a flat panel display device, comprises an anode, a cathode and organic films interposed between the anode and the cathode. The organic films comprise at least a light-emitting layer and further comprise a hole injection layer, a hole transport layer, an electron transport layer, and an electron injection layer, in addition to the light-emitting layer. The organic electroluminescence devices may be classified as a polymer electroluminescence device or a low molecular electroluminescence device depending on the material composing the organic film, particularly the light-emitting layer.
In the organic electroluminescence device, the light-emitting layer should be patterned in order to implement a full coloring, wherein a method for patterning the light-emitting layer includes a method using a shadow mask for a low molecular electroluminescence device, and an ink-jet printing method or a laser induced thermal imaging (LITI) method for the polymer electroluminescence device. Among others, the LITI has the advantages of minutely patterning the organic film as well as performing a dry process instead of a wet process as in the ink-jet printing method.
In order to form the pattern of the polymer organic film using the LITI method, at least a light source, a substrate for an organic electroluminescence device, i.e., an acceptor substrate, and a donor film are required. The donor film comprises a base film, a light-to-heat conversion layer, and a transfer layer composed of an organic film. The patterning of the organic film on the acceptor substrate is performed while a laser from the light source is absorbed into the light-to-heat conversion layer and converted into heat energy. The organic film composing the transfer layer is transferred onto the acceptor substrate by the heat energy.
FIGS. 1A and 1B are cross sectional views showing a transfer mechanism in a general organic film transferring process according to the LITI method.
Referring to FIG. 1A, an organic film S2 is adhered to a donor substrate S1 comprising a base film S1a and a light-to-heat conversion layer S1b by a first adhesion W12 between the donor substrate S1 and the organic film S2. The acceptor substrate S3 is located on the lower part of the donor substrate S1.
Referring to FIG. 1B, a laser having a specific wavelength irradiates a first region R1 except for a second region R2 on the base film S1a. The laser passing through the base film S1a is converted into heat at the light-to-heat conversion layer and the heat causes the change for the first adhesion W12 of the first region R1 to transfer the organic film S2 to the acceptor substrate S3. In the transfer process by the laser, the factors significantly affecting the transfer characteristics of the organic film are the first adhesion W12 between the donor substrate S1 and the organic film S2 in the second region R2, cohesion W22 within the organic film S2, and a second adhesion W23 between the organic film S2 and S3.
In performing the LITI process as described above, the characteristics of the donor film are factors significantly affecting the yield and quality of a product. Among others, the surface roughness of a donor film is one of the important factors since it affects the transfer uniformity.
As illustrated in FIG. 2, when a projection P and/or pore H is generated on the surface of the base film S1a or a barrier lamination is generated on the surface, the laser passing through the base film S1a may be non-uniformly distributed over an entire region on which the process is performed. Thus, scattering, distribution, local concentration and local dilution phenomena of the laser, etc., may occur.
The non-uniformity of the base film surface is inherently generated in the manufacturing process of the base film. Therefore, this non-uniformity can be generated in the base film as well as in any polymer products manufactured by the usual manufacturing processes.
With the non-uniform distribution as above, the transferred organic film can be over-transferred, under-transferred, etc., and the second adhesion between the organic film and the acceptor substrate can be non-uniform. This results in shortened product lifetimes, increased product defect rates, and diminished product quality.